1. Field of the Invention
This invention relates generally to perpendicular magnetic recording systems, and more particularly to perpendicular magnetic recording write heads for use in magnetic recording disk drives.
2. Description of the Related Art
In a perpendicular magnetic recording system like a magnetic recording hard disk drive, the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer. The recording or write head in perpendicular magnetic recording disk drives includes a write pole comprising a shaped pole and a main pole for writing to the recording layer, and one or more return poles for return of magnetic flux from the recording layer.
The main pole is typically formed of high moment magnetic materials, the most common example being iron-cobalt (FeCo) alloys. One of the problems with the high-moment main pole is “erase-after-write”, i.e., the undesirable erasure of information after writing. This is due to the high-moment main pole having a high remanent magnetization or remanence, i.e., the magnetization that remains after the magnetic field is removed.
It is known that remanence can be reduced by forming the main pole as a lamination of multiple magnetic layers. One common lamination approach is the use of an antiferromagnetically coupling (AFC) layer between two magnetic layers. The two antiferromagnetically-coupled magnetic layers have antiparallel magnetizations that substantially cancel each other in the absence of a magnetic field. This results in low main pole remanence and essentially no net magnetic flux at the end that faces the disk, i.e., the air-bearing surface (ABS) of the slider that supports the write head. Antiferromagnetically-coupled laminated main poles have been described with Ru and Cr AFC layers between FeCo and NiFe layers (U.S. Pat. No. 7,057,853; U.S. Pat. No. 7,159,302; U.S. Pat. No. 7,436,629; and U.S. Pat. No. 7,656,611).
In addition to low remanence, the main pole should also have high magnetic permeability for quick response. Generally the magnetic permeability (μ) is defined as μ=dB/dH where B is the magnetic flux and H is the applied magnetic field. The initial permeability is a measure of the ability of the write pole to respond to external magnetic fields as those generated by the write current flowing through the write coil. However, a disadvantage of the laminated main pole with antiferromagnetically-coupled FeCo layers is increased saturation field, and thus decreased permeability.
Another common lamination approach is the use of a non-magnetic layer like NiCr or Al2O3 between two magnetic layers to induce magnetostatic antiparallel coupling (APC) between the two magnetic layers. Thus in the quiescent state (when the write current is off) the moments of the two magnetic layers are antiparallel so there is essentially no net magnetic flux at the end that faces the disk. The antiparallel coupling strength due to insertion of a non-magnetic APC layer is generally weaker than that due to insertion of an AFC layer, and thus higher permeability or lower saturation field, or shorter rise time to saturation can be achieved in a laminated main pole with a non-magnetic APC layer.
It may be desirable for the main pole (MP) to have a tapered trailing edge, i.e., a surface that tapers away from the end that faces the disk. To achieve low remanence for a tapered design, magnetization of the MP needs to be balanced both at the face of the MP that faces the disk and in the regions of the MP recessed from the disk so that there is no net flux emerging from the MP when the write field is off. However, this cannot be achieved with conventional lamination because of the different cross-sectional areas of the end portion of the MP that faces disk and the portion of the MP that is recessed away from the end portion.
What is needed is a perpendicular magnetic recording write head having a laminated main pole with a tapered trailing edge that has low remanence.